Source: How to Clear the Cache Using Functional Administrator? (Doc ID 759038.1)

Note: If you have removed the _pages manually and are facing login issue that’s blank screen.Use the ojspcompile.plperl script to perform a manual pre-compilation of the JSP pages.The following command will compile all the JSP pages and build up the JSP cache again.

perl $FND_TOP/patch/115/bin/ojspCompile.pl –compile –flush -p 2

This utility is also used by the AD utilities to perform this action such as when patches are applied that replace one or more JSP pages